Aluminum alloys for casting, aluminum alloy castings and manufacturing method thereof

Abstract

Aluminum alloys and castings are provided that have excellent practical fatigue resistances. The alloy includes, based upon 100 mass %, 4-12 mass % of Si, less than 0.2 mass % of Cu, 0.1-0.5 mass % of Mg, 0.2-3.0 mass % of Ni, 0.1-0.7 mass % of Fe, 0.15-0.3 mass % of Ti, and the balance of aluminum (Al) and impurities. The alloy has a metallographic structure, which includes a matrix phase primarily of α-Al and a skeleton phase crystallizing around the matrix phase in a network shape. The matrix phase is strengthened by precipitates containing Mg. Because of the strengthened matrix phase, and the skeleton phase that surrounds it, the castings have high strength, high fatigue strength, and high thermo-mechanical fatigue resistance.

Description

INCORPORATION BY REFERENCE

[0001] The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2003-358149 filed on Oct. 17, 2003. The content of the application is incorporated herein by reference in its entirety. FIELD OF THE INVENTION

[0002] The present invention relates to aluminum alloy castings with excellent practical fatigue resistance such as high cycle fatigue strength, and thermo-mechanical fatigue resistance, their manufacturing method, and aluminum alloys for casting suited for the manufacturing. DESCRIPTION OF THE RELATED ART

[0003] An increasing number of automobile components are being made of aluminum alloys as a result of the weight reduction demand. Even the components which are already made of aluminum are being required to be made thinner to reduce their weights. Consequently, higher reliability is demanded for aluminum alloys in terms of strength and fatigue resistance. In particular, aluminum alloys used for automobile engine...

Examples

example 1

(1) Production of Test Pieces

[0061] After preparing molten metal by melting various aluminum alloys of different compositions as shown in table 1, it was poured into a mold for preparing the JIS No. 4 test pieces, left for natural cooling and solidification (casting process). The casting thus obtained was then heated at 530° C. for 5.5 hours and water quenched in a warm water of 50° C. as a solution heat treatment. After this treatment, the casting was further subjected to aging by heating at 160° C. for 5 hours. From the heat treated casting, thermo-mechanical fatigue test pieces No. 1-1 through 1-8 each having a parallel area of 4 mm diameter×6 mm length as shown in Table 1 were produced.

(2) Evaluation of Thermo-Mechanical Fatigue Resistance

[0062] The thermo-mechanical fatigue resistance of each test piece was evaluated as follows.

[0063] Each of the test pieces described above was mounted on the restraint holder made of a low thermal expansion alloy and subjected to a repeti...

example 2

[0067] Test pieces No. 2-1 through 2-6 were prepared as shown in Table 2 using the aluminum alloys for casting of different compositions in a similar manner as in Embodiment No. 1. These test pieces have different amount of Mg.

[0068] Hardness of the test pieces was measured and the hardness measurement was conducted using a Vickers Hardness Tester or a Micro Vickers Hardness Tester. The “Total Mean Hardness”, shown in Table 2, was measured by creating a large indentation with a load of 10 kgf and a loading time of 30 sec and represents a mean hardness of the entire test piece. The “Initial Hardness of Matrix Phase” was measured by creating a small indentation in the center of the matrix phase with a load of 100 g and a loading time of 30 sec on the test piece prior to heating. The “Hardness of Matrix Phase after Heating” is the hardness of the matrix after heating it at 250° C. for 100 hr and is measured in a similar manner as the “Initial Hardness of Matrix Phase” mentioned above....

example 3

[0074] Test pieces No. 3-1 through 3-3 were prepared as shown in Table 3 using different compositions of the aluminum alloys for casting as in Example 1. These test pieces have different Cu contents.

[0075] A salt water spraying test was applied to these test pieces and the corrosion resistance characteristics of these test pieces are evaluated. The salt water spraying test was conducted in accordance with JIS Z2371-1994 for 100 hours, maintaining the salt water concentration to 5% and the temperature of the spraying salt water to 35° C. The surfaces of the test pieces were polished prior to the test using #600 water resistant grinding paper.

[0076] FIGS. 2 (a)-2(c) show surface photographs of test pieces No. 3-1 through No. 3-3 washed after the salt water spraying test. It can be seen that the test pieces with higher Cu contents are corroded severely, while almost no corrosions exist in the test pieces with low Cu contents. Test piece No. 3-1, which contains less that 0.2 mass % of...

INCORPORATION BY REFERENCE

[0001] The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2003-358149 filed on Oct. 17, 2003. The content of the application is incorporated herein by reference in its entirety. FIELD OF THE INVENTION

[0002] The present invention relates to aluminum alloy castings with excellent practical fatigue resistance such as high cycle fatigue strength, and thermo-mechanical fatigue resistance, their manufacturing method, and aluminum alloys for casting suited for the manufacturing. DESCRIPTION OF THE RELATED ART

[0003] An increasing number of automobile components are being made of aluminum alloys as a result of the weight reduction demand. Even the components which are already made of aluminum are being required to be made thinner to reduce their weights. Consequently, higher reliability is demanded for aluminum alloys in terms of strength and fatigue resistance. In particular, aluminum alloys used for automobile engine...

Examples

example 1

(1) Production of Test Pieces

[0061] After preparing molten metal by melting various aluminum alloys of different compositions as shown in table 1, it was poured into a mold for preparing the JIS No. 4 test pieces, left for natural cooling and solidification (casting process). The casting thus obtained was then heated at 530° C. for 5.5 hours and water quenched in a warm water of 50° C. as a solution heat treatment. After this treatment, the casting was further subjected to aging by heating at 160° C. for 5 hours. From the heat treated casting, thermo-mechanical fatigue test pieces No. 1-1 through 1-8 each having a parallel area of 4 mm diameter×6 mm length as shown in Table 1 were produced.

(2) Evaluation of Thermo-Mechanical Fatigue Resistance

[0062] The thermo-mechanical fatigue resistance of each test piece was evaluated as follows.

[0063] Each of the test pieces described above was mounted on the restraint holder made of a low thermal expansion alloy and subjected to a repeti...

example 2

[0067] Test pieces No. 2-1 through 2-6 were prepared as shown in Table 2 using the aluminum alloys for casting of different compositions in a similar manner as in Embodiment No. 1. These test pieces have different amount of Mg.

[0068] Hardness of the test pieces was measured and the hardness measurement was conducted using a Vickers Hardness Tester or a Micro Vickers Hardness Tester. The “Total Mean Hardness”, shown in Table 2, was measured by creating a large indentation with a load of 10 kgf and a loading time of 30 sec and represents a mean hardness of the entire test piece. The “Initial Hardness of Matrix Phase” was measured by creating a small indentation in the center of the matrix phase with a load of 100 g and a loading time of 30 sec on the test piece prior to heating. The “Hardness of Matrix Phase after Heating” is the hardness of the matrix after heating it at 250° C. for 100 hr and is measured in a similar manner as the “Initial Hardness of Matrix Phase” mentioned above....

example 3

[0074] Test pieces No. 3-1 through 3-3 were prepared as shown in Table 3 using different compositions of the aluminum alloys for casting as in Example 1. These test pieces have different Cu contents.

[0075] A salt water spraying test was applied to these test pieces and the corrosion resistance characteristics of these test pieces are evaluated. The salt water spraying test was conducted in accordance with JIS Z2371-1994 for 100 hours, maintaining the salt water concentration to 5% and the temperature of the spraying salt water to 35° C. The surfaces of the test pieces were polished prior to the test using #600 water resistant grinding paper.

[0076] FIGS. 2 (a)-2(c) show surface photographs of test pieces No. 3-1 through No. 3-3 washed after the salt water spraying test. It can be seen that the test pieces with higher Cu contents are corroded severely, while almost no corrosions exist in the test pieces with low Cu contents. Test piece No. 3-1, which contains less that 0.2 mass % of...

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